lexq_ab_test_startStart an A/B test on a policy group. Requires a challenger version ID and traffic rate. The split is computed from context.trafficKey on each execution request; requests that omit it never reach the challenger and the test stays at 0%.
| Name | Required | Description | Default |
|---|---|---|---|
| groupId | Yes | Policy group ID | |
| trafficRate | Yes | Traffic percentage routed to challenger (1-99) | |
| testVersionId | Yes | Challenger version ID to test |
Changes observed during successful MCP inspections.
Input schema / $schemaPrevious value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"Input schema / additionalPropertiesRemoved value: -falseInput schema / properties / groupId / patternAdded value: +"^([0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[1-8][0-9a-fA-F]{3}-[89abAB][0-9a-fA-F]{3}-[0-9a-fA-F]{12}|00000000-0000-0000-0000-000000000000|ffffffff-ffff-ffff-ffff-ffffffffffff)$"Input schema / properties / testVersionId / patternAdded value: +"^([0-9a-fA-F]{8}-[0-9a-fA-F]{4}-[1-8][0-9a-fA-F]{3}-[89abAB][0-9a-fA-F]{3}-[0-9a-fA-F]{12}|00000000-0000-0000-0000-000000000000|ffffffff-ffff-ffff-ffff-ffffffffffff)$"Input schema / properties / challengerVersionIdRemoved value: -{
- "description": "Challenger version ID",
- "format": "uuid",
- "type": "string"
-}Input schema / properties / challengerWeightRemoved value: -{
- "description": "Challenger traffic weight (%)",
- "maximum": 99,
- "minimum": 1,
- "type": "integer"
-}Input schema / properties / controlWeightRemoved value: -{
- "description": "Control traffic weight (%)",
- "maximum": 99,
- "minimum": 1,
- "type": "integer"
-}Input schema / properties / identityKeyRemoved value: -{
- "description": "Fact key for sticky assignment (e.g. customer_id)",
- "type": "string"
-}Input schema / properties / testVersionIdAdded value: +{
+ "description": "Challenger version ID to test",
+ "format": "uuid",
+ "type": "string"
+}Input schema / properties / trafficRateAdded value: +{
+ "description": "Traffic percentage routed to challenger (1-99)",
+ "maximum": 99,
+ "minimum": 1,
+ "type": "integer"
+}Input schema / requiredPrevious value: -[
- "groupId",
- "challengerVersionId",
- "controlWeight",
- "challengerWeight"
-]New value: +[
+ "groupId",
+ "testVersionId",
+ "trafficRate"
+]Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already indicate a mutation (readOnlyHint=false) and non-destructive (destructiveHint=false). The description adds a critical behavioral detail about context.trafficKey and its effect on traffic splitting, which goes beyond annotations. It does not cover other side effects like overwriting an existing test, but the added detail is valuable.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two concise sentences, front-loaded with the purpose and requirements, followed by a crucial behavioral caveat. Every sentence earns its place with no redundancy.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a start operation with 3 required params and no output schema, the description covers the core function and the most important runtime behavior (trafficKey). It does not mention what happens to an existing test or success/failure responses, but given the tool's simplicity, it is largely sufficient.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100%, so the schema already documents all three parameters. The description restates the purpose of testVersionId and trafficRate but adds no new format, constraints, or relationships beyond what the schema provides.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description clearly states the verb 'Start' and the resource 'A/B test on a policy group', and identifies the required inputs. It does not explicitly differentiate from sibling tools like adjust or stop, but the purpose is unambiguous.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description implies usage (start a test) but does not explicitly state when to use this versus the sibling adjust/stop tools. It mentions prerequisites (challenger version ID, traffic rate) but no exclusions or alternative routing.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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